Tubular heat exchangers

ABSTRACT

A tubular heat exchanger of the general type including a fixed tube plate, a floating tube plate, tubes extending between the tube plates and baffles on the tubes, has a reinforcing member of non-circular section extending through non-circular apertures in the baffles, to prevent collapse of the tubes under an axial compressive load, by preventing the baffles from rotating relative to one another.

[ Sept. 23, 1975 United States Patent [19] Moss et al.

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Assistant Examiner-Theophill W. Streule Jr. N I App] 0 363 102 Attorney, Agent, or Fzrm-Holman & Stern Related US. Application Data [63] Continuation-impart of Ser. No. 122,455, March 9,

i971, abandoned.

ABSTRACT Foreign Application Priority Data Apr. 21, 1970 United Kingdom..........

.. 18979/ A tubular heat exchanger of the general type including a fixed tube plate, a floating tube plate, tubes extending between the tube plates and baffles on the tubes,

[51] Int. F28b 9/00 has a reinforcing member of non-circular section ex- 122/32, 34, 510; tending through non-circular apertures in the baffles,

[58] Field of Search........................

165/159-162, 26-80 to prevent collapse of the tubes under an axial compressive load, by preventing the baffles from rotating relative to one another.

[56] References Cited UNITED STATES PATENTS 1,992,504 2/1935 Penniman....................... 165/162 X 14 Claims, 7 Drawing Figures US Patent Sept. 23,1975 Sheet 1 on 3,907,030

US Patent Sept. 23,1975 Sheet 2 of4 3,907,030

n v n l l u I v v v I u I u u US Patent Sept. 23,1975 Sheet 3 of4 3,907,030

US Patent Sept. 23,1975 Sheet 4 of4 3,907,030

Pat. application Ser. No. l22455 filed TUBULAR HEAT EXCHANGERS This application is a continuation-in-part of our US. Mar. 9th, l97l now abandoned.

BACKGROUND OF THE INVENTION This invention relates to tubular heat exchangers.

PRIOR ART Tubular heat exchangers are known in which a plurality of tubes are anchored at their opposite ends in tube plates which are located in a housing which is usually of cylindrical form. The tube plates divide the interior of the housing into three chambers through the center one of which one fluid to take part in the heat exchange process. is passed. The other fluid is introduced into one of the end chambers, passes through the tubes and leaves the heat exchanger from the other end chamber,.

Because there may be differential expansion effects during temperature changes, it is customary to allow one of the tube plates to float axially of the housing. It will be readily appreciated, therefore, that when the fluid in the center chamber is at a lower pressure than the fluid passing through the tubes, there will be a compressive load applied to the tube stack, i.e., to the assembly of the tubes and tube plates.

In aircraft applications. space and weight are at a premium and it is therefore often found necessary to make up the tube stack from a very large number of small diameter, very thin walled tubes, so that the tube stack tends to have a very low strength in compression. Unfortunately many modern aircraft applications have the fluid in the central chamber at low pressure and the fluid passing through the tubes at very high pressure. Thus it is extremely difficult to produce a compact lightweight aircraft heat exchanger of high performance.

It has long been customary also to utilize baffles located on the tubes to direct the flow of fluid through the center chamber in a sinuous fashion, crossing the tubes repeatedly. Various arrangements using D- shaped baffles and "disc and donut" baffles have been evolved for this purpose. The baffles are spaced apart, usually by spacers on some of the tubes, although other baffle spacing arrangements have been proposed.

SUMMARY OF INVENTION We have observed that when a tube stack including baffles is subjected to a compressive force, axial collapse of the stack is always accompanied by rotations of the baffles about the axis of the tube stack relative to one another and also relative to the tube plates. During such collapse. the individual tubes bend, but since they are tied together at intervals by the baffles and the baffles are themselves confined within the housing, this bending is limited to twisting of the tube stack.

Our invention therefore resides in the application of this observation to prevent the rotation of the baffles relative to one another and thereby to stiffen the tube stack against collapse.

A tubular heat exchanger in accordance with the invention comprises the combination of:

a housing of generally cylindrical form;

a pair of tube plates in the housing, one of which is free to move axially of the housing, said tube plates defining a center chamber in the housing and a pair of end chambers;

a matrix consisting of a plurality of light tubes joined to and extending between said tube plates and interconnecting said end chambers;

a plurality of baffles in spaced relationship on the tubes between the tube plates, said baffles slidably engaging the interior of the housing and defining a sinuous flow path over said tubes for a fluid flowing through said center chamber;

spacer means maintaining the baffles in spaced relationship;

and at least one elongated reinforcing member which is of relatively substantial cross-sectional dimensions as compared with the tubes so as to be relatively rigid as compared with the tubes, said reinforcing member being of non-circular cross-section and extending through complementary non-circular apertures in the baffles so as to prevent relative rotation between the baffles.

BRIEF DESCRIPTION OF DRAWINGS In the accompanying drawings:

FIG. I is a somewhat diagrammatic longitudinal cross section of an example of a heat. exchanger constructed in accordance with the invention;

FIG. 2 is a section on line 2-2 in FIG. I;'

FIG. 3 is an enlarged fragmentary section on line 3-3 in FIG. 1;

FIG. 4 is an enlarged fragmentary section on line 44 in FIG. 1;

FIG. 5 is a fragmentary longitudinal section of a modifed form of the heat exchanger of FIGS. 1 to 5;

FIG. 6 is a fragmentary longitudinal section showing another example of the invention; and

FIG. 7 is a section on line 77 in FIG. 6.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring first to FIGS. 1 to 4 of the drawings, the heat exchanger shown comprises a housing which is formed in two parts namely a cylindrical tubular shell 10 having an integral end wall 11, and an end member 12. A pair of tube plates 13, 114 are provided and of these plate 13, is fixed, being clamped between the end of the shell 10 and the end member 12 and the plate 14, is slidable axially of the shell 10. This latter tube plate 14 is provided with a peripheral sealing element 15 which seals the clearance which exists between the shell 10 and the tube plate 14. The tube plates l3, 14 separate the interior of the housing into a center chamber 16 and a pair of end chambers 17, 18. These end chambers have ports 17a, 17a respectively.

Secured to the tube plates l3, l4 and extending therebetween are a plurality of light, thin walled tubes 19. These tubes 19 have their ends sealingly engaged in bores through the end plates. The number and relative dispositions of the tubes are shown in FIG. 2 where only a few of the tubes are actually drawn in. the remainder being represented merely by dots.

The heat exchanger is provided with a disc and donut baffle arrangement, comprising two sets of baffles 20, 2I arranged alternately in spaced relationship between the tube plates 13, 14. The baffles 20 are of annular configuration having an external diameter only slightly less than the internal diameter of the shell 10, and a central aperture 22. The baffles 21 are discs of a diame' ter substantially smaller than the internal diameter of 3 the shell, but provided with a plurality .of integral lobes 23 which engage the interior of the shell to locate the baffles centrally therein.

The shell has ports 24, adjacent its ends through which fluid flow through the chamber 16 is established. Such flow is constrained by the baffles 20, 21 to a sinuous path alternately radially inwards towards the aperture 22 and radially outwardly towards the spaces between the peripheries of the baffles 21 and the interior of the shell. Thus the flow repeatedly crosses and reerosses the tubes 19.

The baffles 20, 21 are maintained in their spaced relationship by spacer tubes 26 on some of the tubes 19. Only a few of the tubes 19 have spacer tubes. namely the nine tubes marked with black quadrants in FIG. 2. This number is deliberately kept small since the heat transfer efficiency of any tube 19 surrounded by spacer tubes 26 is clearly reduced. For the same reason the tubes 26 are lightweight.

To avoid difficulties which may occur as a result of differential thermal expansion, the tubes 26 are deliberately out slightly short, i.e., the sum of the total length of the tubes 26 and the total of the thickness of the baffles 20, 21 is less than the spacing between the tube plates 13, 14. Exact position of the baffles in the shell 10 is not critical.

To reinforce the tube stack consisting of the tubes 19, the tube plates 13, 14 and the baffles 20, 21, there are provided a plurality of elongated reinforcing members 27 which extend through apertures cut in the baffles 20, 21. These members 27 are of rectangular crosssection and are of cross-sectional dimensions substantially greater than those of the tubes 19, thereby rendering these members very much more rigid than the tubes 19. The members 27 extend through complementary rectangular holes in the baffles 20, 21. These members 27 are arranged around the exterior of the tube stack and the holes in the baffles 21 are, in fact, in the lobes 23 therein. Thus each and every one of the baffles 20, 21 is engaged by all of the members 27. This has the effect of preventing the baffles 20, 21 from rotating about the axis of the tube bundle.

The members 27 are only very slightly shorter than the spacing between the tube plates 13, 14. This is necessary to overcome any differential thermal expansion problems which may arise. The arrangement is such, therefore, that the members 27 are capable of abutting directly against the tube plates 13, 14 and postively preventing axial collapse of the tube stack.

In addition, a plurality of pairs of abutments 28, 29 are provided on each tube plate l3, 14 to coact with the members 27. As shown in FIG. 4 these abutments define between them a space capable of receiving the end of the member 27 between them. The abutments have a pair of adjacent parallel faces which are spaced by a distance only slightly larger than the width of the member 27. The abutments 28 and 29 therefore not only locate the tube plate 13 and 14 relative to the members 27 but also prevent the members 27 from twisting relative to the tube plates.

In use, when the heat exchanger is used, for example. to cool lubricating oil with high a pressure coolant in an aircraft engine lubricating system, the oil is introduced through the port 24 and leaves through the port 25. The coolant on the other hand, enters through the port 18a and leaves through the port 17a. The high pressure coolant acts on the two tube plates 13, 14 and since the tube plate 14 is free to move like a piston, a substantial compressive load is applied to the tube stack. In the absence of the members 27, the tube stack would collapse under this load, each tube bowing and eventually buckling in the region of one of the baffles 20, 21. By preventing relative rotation of the baffles 20, 21, the members 27 stiffen the tube stack very substantially and collapse of the stack is very unlikely. In the event that abnormally high coolant pressures are encountered and collapse of the tube stack does commence, the members 27 will abut directly against the tube plates and accept the axial compressive load directly.

It should be noted that the members 27 do not interfere with any effects which may arise as a result of differential thermal expansion in the heat exchanger. The members 27 are not secured to any part of the heat exchanger, being slidable in the apertures in the baffles and not attached to the tube plates. Even after the pos sible slight collapse of the stack referred to above, there will still be scope for differential expansion within the heat exchanger since, in this partially collapsed condition, the tubes 19 will be bowed between adjacent baffles and slight relative movement of the various parts of the heat exchanger can be accommodated by straightening 0f the tubes 19.

Moreover, it will be noted that the reinforcing members 27 lie outside the tube bundle, i.e., the inclusion of the members 27 has not necessitated the omission of a significant number of tubes. In a disc and donut baffle arrangement the provision of a sufficient area for flow between the disc baffles 21 and the internal surface of the shell 10 presents no great problem so that the addition of the lobes 23 to engage the shell and receive the members 27 does not create any difficulty.

In the modified form of the invention shown in FIG. 5, the members 27 and the tube plates 13, 14 are formed with aligned'blind bores which receive locating dowels 30. Each end of each member 27 may have one or two such dowels 30. In the former case, the dowel merely acts to locate the tube relative to the member 27, whereas, in the second case, the dowels also prevent twisting of the member 27 relative to the tube plate.

Turning finally to FIGS. 6 and 7 the alternate em bodiment shown therein utilizes a single longitudinal reinforcing member 31 extending along the axis of the tube stack. In this case, the invention is shown as applied to a heat exchanger employing D-shaped baffles 32. The member 31 inthis case is in the form of a tube of substantial diameter and wall thickness. Moreover, the member 31 is provided with a pair of diametrically opposite external ribs 33 so that the member 31 is externally of non-circular cross-sectional configuration. To provide the required non-rotatable connection between the member 31 and the baffles 32, the latter have In the embodiments of FIGS. 6 and 7 the arrangement for spacing the baffles 32is exactly the same as that utilized in the embodiment of FIGS. 1 to 4.

It will, of course, be appreciated that it is quite possible to use rectangular reinforcing members 27 in a D- type baffle tube stack although only two members 27 would be used. Furthermore, it would also be possible to utilize a central tubular reinforcing member 31 in a disc and donut type tube stack although in this case the member 31 would engage alternate baffles, the discs, only.

We claim:

l. A tubular heat exchanger comprising the combination of a housing of generally cylindrical form;

a pair of tube plates inthe housing, one of which is free to move axially of the housing, said tube plates defining a center chamber in the housing and a pair of end chambers;

a matrix consisting of a plurality of light tubes joined to and extending between said tube plates and interconnecting said end chambers;

a plurality of baffles in spaced relationship on the tubes between the tube plates, said baffles slidably engaging the interior of the housing and defining a sinuous flow path over said tubes for a fluid flowing through said center chamber;

spacer means maintaining the baffles in spaced relationship;

and at least one elongated reinforcing member which is of relatively substantial cross-sectional dimensions as compared with the tubes so as to be relatively rigid as compared with the tubes, said reinforcing member being of non-circular cross-section and extending through complementary noncircular apertures in the baffles so as to prevent rel ative rotation between the baffles said reinforcing member being of a length relative to said tubes and functioning to define a minimum distance between said tube plates for preventing axial collapse of said tubes.

2. A tubular heat exchanger as claimed in claim 1 further comprising interengaging means for locating the reinforcing members relative to the tube plates.

3. A tubular heat exchanger as claimed in claim 1 in which there are a plurality of said reinforcing members arranged in spaced relationship around the periphery of the tube matrix.

. 4. A tubular heat exchanger as claimed in claim 3 in lar cross-section.

5. A tubular heat exchanger as claimed in claim 4 further comprising a plurality of pairs of abutments provided on the tube plates to coact with the adjacent ends of the respective reinforcing members so as to locate which each of said reinforcing members is of rectanguthe tube plates relative to the reinforcing members.

6. A tubular heat exchanger as claimed in claim 5 in which each pair of abutments. has a pair of adjacent parallel faces spaced by a distance only slightly greater than the width of the associated reinforcing member, so as to prevent twisting of the associated member relative to the tube plate.

7. A tubular heat exchanger as claimed in claim 4 in which the reinforcing members are only slightly shorter than the distance between the adjacent faces of the tube plates, whereby in the event of a compressive loading causing collapse of the matrix to commence the tube plates engage the reinforcing members which then directly accept compressive load.

8. A tubular heat exchanger as claimed in claim 4 in which the baffles are altemately in the form of discs and annuli, the disc baffles being provided with integral lobes to engage the interior of the housing and the apertures which receive the reinforcing members being formed in said lobes.

9. A tubular heat exchanger as claimed in claim 4 in which the ends of the reinforcing members and the tube plates are formed with aligned blind bores, and in which there is provided a plurality of locating dowels engaged in the blind bores to locate the tube plates relative to the reinforcing members.

10. A tubular heat exchanger as claimed in claim 1 in which said reinforcing member extends along the axis of the housing.

11. A tubular heat exchanger as claimed in claim 10 in which the reinforcing member is of generally cylindrical configuration but is provided with a plurality of external ribs.

12. A tubular heat exchanger as claimed in claim 10 in which there are a pair of ribs on the reinforcing member at diametrically opposite positions.

13. A tubular heat exchanger as claimed in claim 12 in which each tube plate is formed with a slot and the ends of the reinforcing member have axially projecting portions which are received by said slot to prevent twisting of the reinforcing member relative to the tube plates.

14. A tubular heat exchanger as claimed in claim 1 in which there are a plurality of said reinforcing mem-' bers arranged in spaced relationship around the periphery of the tube matrix, each of said reinforcing members being of rectangular cross-section, the baffles being alternately in the form of discs and annuli, the disc baffles being provided with integral lobes equally spaced about the axis of the center chamber to engage the interior of said chamber and the apertures which receive the reinforcing members being formed in said 

1. A tubular heat exchanger comprising the combination of a housing of generally cylindrical form; a pair of tube plates in the housing, one of which is free to move axially of the housing, said tube plates defining a center chamber in the housing and a pair of end chambers; a matrix consisting of a plurality of light tubes joined to and extending between said tube plates and interconnecting said end chambers; a plurality of baffles in spaced relationship on the tubes between the tube plates, said baffles slidably engaging the interior of the housing and defining a sinuous flow path over said tubes for a fluid flowing through said center chamber; spacer means maintaining the baffles in spaced relationship; and at least one elongated reinforcing member which is of relatively substantial cross-sectional dimensions as compared with the tubes so as to be relatively rigid as compared with the tubes, said reinforcing member being of non-circular crosssection and extending through complementary non-circular apertures in the baffles so as to prevent relative rotation between the baffles said reinforcing member being of a length relative to said tubes and functioning to define a minimum distance between said tube plates for preventing axial collapse of said tubes.
 2. A tubular heat exchanger as claimed in claim 1 further comprising interengaging means for locating the reinforcing members relative to the tube plates.
 3. A tubular heat exchanger as claimed in claim 1 in which there are a plurality of said reinforcing members arranged in spaced relationship around the periphery of the tube matrix.
 4. A tubular heat exchanger as claimed in claim 3 in which each of said reinforcing members is of rectangular cross-section.
 5. A tubular heat exchanger as claimed in claim 4 further comprising a plurality of pairs of abutments provided on the tube plates to coact with the adjacent ends of the respective reinforcing members so as to locate the tube plates relative to the reinforcing members.
 6. A tubular heat exchanger as claimed in claim 5 in which each pair of abutments has a pair of adjacent parallel faces spaced by a distance only slightly greater than the width of the associated reinforcing member, so as to prevent twisting of the associated member relative to the tube plate.
 7. A tubular heat exchanger as claimed in claim 4 in which the reinforcing members are only slightly shorter than the distance between the adjacent faces of the tube plates, whereby in the event of a compressive loading causing collapse of the matrix to commence the tube plates engage the reinforcing members which then directly accept compressive load.
 8. A tubular heat exchanger as claimed in claim 4 in which the baffles are alternately in the form of discs and annuli, the disc baffles being provided with integral lobes to engage the interior of the housing and the apertures which receive the reinforcing members being formed in said lobes.
 9. A tubular heat exchanger as claimed in claim 4 in which the ends of the reinforcing members and the tube plates are formed with aligned blind bores, and in which there is provided a plurality of locating dowels engaged in the blind bores to locate the tube plates relative to the reinforcing members.
 10. A tubular heat exchanger as claimed in claim 1 in which said reinforcing member extends along the axis of the housing.
 11. A tubular heat exchanger as claimed in claim 10 in which the reinforcing member is of generally cylindrical configuration but is provided with a plurality of external ribs.
 12. A tubular heat exchanger as claimed in claim 10 in which there are a pair of ribs on the reinforcing member at diametrically opposite positions.
 13. A tubular heat exchanger as claimed in claim 12 in which each tube plate is formed with a slot and the ends of the reinforcing member have axially projecting portions which are received by said slot to prevent twisting of the reinforcing member relative to the tube plates.
 14. A tubular heat exchanger as claimed in claim 1 in which there are a plurality of said reinforcing members arranged in spaced relationship around the periphery of the tube matrix, each of said reinforcing members being of rectangular cross-section, the baffles being alternately in the form of discs and annuli, the disc baffles being provided with integral lobes equally spaced about the axis of the center chamber to engage the interior of said chamber and the apertures which receive the reinforcing members being formed in said lobes. 